Although an old question, the answer might help someone else who stumbles across it. The quota related information is contained in the headers of the response to your request. Each API endpoint seems to have its own limit.
Here's an example of a response that still has something left of the quota:
{'allow': 'GET', 'Content-Encoding': 'gzip', 'Content-Type': 'application/xml;charset=UTF-8', 'Date': 'Fri, 26 Aug 2019 17:46:46 GMT', 'Server': 'Apache-Coyote/1.1', 'vary': 'Origin', 'X-ELS-APIKey': 'your-api-key-would-be-here', 'X-ELS-ReqId': '16385g19-b193-1308-5817-c5694db5619g', 'X-ELS-ResourceVersion': 'default', 'X-ELS-Status': 'OK', 'X-ELS-TransId': '16385g19-b193-1308-5817-c5694db5619g', 'X-RateLimit-Limit': '20000', 'X-RateLimit-Remaining': '19636', 'X-RateLimit-Reset': '2019-10-03 07:18:17', 'transfer-encoding': 'chunked', 'Connection': 'keep-alive'}
Here's an example for which the quota has been exceeded:
{'Content-Encoding': 'gzip', 'Content-Type': 'text/xml;charset=UTF-8', 'Date': 'Fri, 19 Aug 2019 17:46:46 GMT', 'Server': 'Apache-Coyote/1.1', 'X-ELS-Status': 'QUOTA_EXCEEDED - Quota Exceeded', 'X-RateLimit-Reset': '2019-08-26 05:51:01', 'Content-Length': '191', 'Connection': 'keep-alive'}
An example to get the headers in python using requests:
url = https://api.elsevier.com/content/abstract/scopus_id/85040730407?apiKey=yourapikey
response = requests.get(url)
print(response.headers)